1. Field of the Invention
This invention generally relates to method and apparatus for correcting errors in the output of a rate gyro and is especially useful for measuring the heading changes of a turning vehicle (e.g., a banked and turning aircraft in flight). The invention provides a relatively simple and economical heading reference signal source for use in vehicles (e.g., aircraft).
The invention is particularly suited for use with a StrikeFinder.TM. storm monitoring system by Insight Instrument Corporation (e.g., see U.S. Pat. No. 5,245,274 hereby incorporated by reference) so as to provide aircraft heading data to permit the displayed lightning strikes to be correctly oriented on the display with respect to the current instantaneous aircraft heading.
2. Description of the Prior Art
Aircraft heading reference systems typically utilize a spinning gyroscope mass for an inertial reference. Such a "gyro-compass" is in common usage despite its relatively large size, high cost, poor long-term reliability and routine required maintenance. For some applications, such complicated and expensive devices are effectively impractical.
A type of gyroscope called a "rate gyro" is also available in many forms. Some rate gyros utilize a traditional spinning wheel (and thus may be subject to the same impracticalities as traditional gyro-compass explained above) while others may use a simple stream of air, a tuning fork, a taunt wire or the like for an inertial reference. In its most common form, a rate gyro typically senses the rate of rotation around a predetermined axis and delivers a voltage or resistance change functionally related in a predetermined way to the turn rate (i.e., the first order derivative of the turn angle taken with respect to time) of the vehicle to which the rate gyro is attached.
Piezoelectric vibrating gyroscopes are among the known types of rate gyros presently available in the commercial market. Such gyroscopes have been described in the literature (e.g., see Nakamura, "Piezoelectric Free-Free-Bar Vibration Gyroscope"). The exemplary embodiment of this invention uses the GYROSTAR.TM. Piezoelectric Vibrating Gyroscope ENX-0011 available from Murata Mfg. Co. Ltd.
Relatively economic accelerometers are also known in the art and commercially available. For example, the exemplary embodiment of this invention utilizes a capacitive accelerometer Model 1010 available from Silicon Designs, Inc.
It is also generally known in the aircraft industry that when an aircraft in flight undergoes a coordinated banked turn, the aircraft experiences an increased gravity or G-force along its vertical axis related to the bank angle .theta. by the following equation: EQU G.sub.force =1/(cosine .theta.) Equation (1)